In the field of data communications, the Open Systems Interconnection (OSI) Reference Model, also known as the OSI seven-layer model, defines a conceptual framework for communications protocol design. The OSI Reference Model breaks down the communications task into seven, ostensibly independent, layers of peer-to-peer functionality. The ISO-OSI 7 layer Reference Model is more formally known as ISO Standard 7498, 1984, 7498-1:1994, and CCITT standard X.200.
Each layer of the OSI model only uses the functions of a layer directly below it, and only exports functionality to a layer directly above it. This abstract, independent-layered, approach simplifies design, analysis and implementation of complex communications protocols and associated system interactions, facilitating standardisation and thus vendor inter-operability.
A system implementing protocol behaviour conforming to a series of these layers is known as a protocol stack. Protocol stacks can be implemented either in hardware, firmware, software, or a combination of two or more of these. Typically, lower layers of the OSI model, which are closely associated with the low-level, high-speed, physical operation of a communications network are implemented in hardware, the higher layers being implemented in software.
However, in some circumstances, it is desirable to by-pass the strict functional layered-approach of the OSI Reference Model. In this respect, so-called “cross-layer” communication mechanisms, i.e. inter-layer signalling mechanisms, have been proposed to, for example, provide improved media access control, superior resource reservation control, and more efficient service dependent data transfer through different types of networks than is presently enjoyed. Efficient Transmission Control Protocol (TCP) over wireless media or fast-handover functionality in wireless networks are examples of useful applications of such cross-layer communications mechanisms. Examples of cross-layer communication mechanisms are described in “A Suggested QoS Architecture for Multimedia Communications” (A. Campbell, G. Coulson, F. Garcia, D. Hutchison, H. Leopold, N. Singer, ISO/IEC JTC1/SC21A/WGI N1201, 15-9-92, BSI/IST 21/-/1/51738, BSI/IST/21/-/5/62, 15p. (OSI95/LANC/A*/01/TR/P/V1, September 1992, MPG-92-37)), and “Integrated Quality of Service for Multimedia Communications” (A. Campbell, G. Coulson, F. Garcia, D. Hutchison and H. Leopold, IEEE INFOCOM 93, San Francisco, March 1993).
However, the known existing cross-layer communication mechanisms require a separate tangible communications channel between layers of the OSI model in order to communicate signalling and control data between the layers of the OSI model. Additionally, no standard, widely accepted, interfaces for inter-layer signalling and control data communications exist. Further, communication of inter-layer signalling and control data between hardware and software layers cannot readily be implemented. Also, known mechanisms lack synchronization of state (of a given layer) across layers, the state information relating to a given functionality at one layer may help in making better-informed decisions at another, upper, layer when performing similar or related functionality. For example, the Data Link layer protocol of a WiFi device performs functions to detect mobility, and attach a mobile device to a new cell when required while roaming. In this respect, layer 3 (the Network layer) at the IP level performs similar functions, but performance of these functions is dissociated with those of layer 2 (the Data Link layer).